1. Field of the Invention
The subject invention is directed to coating compositions which are applicable in the field of construction materials. The invention is particularly applicable to the field of high-rise construction based on steel infrastructure where it is desired to provide fireproofing and/or acoustical insulation.
2. Description of the Related Art
Thick coatings of inorganic materials have been commonly applied in the course of the erection of steel structures designed to serve as multi-story building infrastructure primarily to serve in a fireproofing capacity, as well as to function as acoustic insulation agents. In the event of a major fire in a section or on one or more floors of a building, it has been found that such coatings substantially inhibit thermal weakening of the steel infrastructure and, thus, prevent a catastrophic collapse of the building.
In order to be suitable for such use, coating mixes, both in the wet and dry state, must possess a number of crucial properties. They must be able to hold the large quantity of water that renders them capable of being pumped easily and to great heights. Although high water content is desired, the aqueous dispersion must retain a consistency sufficient to prevent segregation or settling of ingredients and permit adequate "yield" or uniform coverage on the steel surface at a given thickness. Furthermore, the coating mixtures must obviously be capable of adhering to steel surfaces, both in the slurried state and upon drying. Finally, the mixtures must set without any undue expansion or shrinkage which could result in the formation of cracks that would seriously detract from the insulating value of the dry coating. This complex balance of properties has substantially been achieved heretofore by gypsum-vermiculite systems containing cellulosic fiber. Examples of compositions of this general type are described by Bragg in U.S. Pat. Nos. 3,719,573 and 3,839,059. However, vermiculite as a naturally occurring mineral is subject to variations in quality, uniformity and consistency.
In order to overcome the deficiencies encountered with vermiculite-based mixtures, compositions containing synthetic and natural organic particulate material have been suggested (See U.S. Pat. No. 4,751,024). Due to the hydrophobic nature of the organic material, the composition's properties are very sensitive to the water content used in forming the sprayable mix. Thus, when a low water content is used, it is difficult to form a uniform fluid mixture which is capable of being readily pumped to the desired point of application. When the water content is increased to achieve a mixture of lower viscosity (and thus readily mixable and pumpable), the resultant mixture exhibits a high flow at the point of application and, thus, does not readily maintain its shape and adhere to the infrastructural surface. Such formulations may fall off at the surface and, thereby, lose the advantages achievable by the coating.
Various agents are known to thicken formulations e.g. polyethylene oxide, xanthan gum, carboxymethyl cellulose guar gum, hydroxypropyl guar gum. Although such agents may provide a less fluid composition at the point of application and thereby aid in initial adhesion, they are not desirable for the instant application as they impair the ability of providing a uniform initial mix and require more energy (larger pumps) to force the fluid through the conduit to the point of application. Further, such thickeners, in many instances, do not impart good adhesion properties to compositions containing them.
Other agents are known to impart thixotropic properties to fluids. These agents include attapulgite and sepiolite clays which are conventionally provided as ultrafine colloidal material. For example, U.S. Pat. Nos. 3,986,969 and 4,801,395 describe the use of attapulgite as a thixotropic agent while JP 63-297256 teaches the use of sepiolite as a thixotropy-imparting agent for an inorganic adhesive spray composition. The use of thixotropic agents would detract from the instant formulation. They would provide high viscosity under the low shear mixing conditions. The formulator would not be able to provide a uniform composition or would be required to add excess water at the mixing stage which would cause a high flow coating to be applied.
It is highly desired to provide a fireproofing and acoustical dampening composition which, when initially mixed with water at the job site, exhibits low viscosity to allow the components to readily mix and form a uniform composition while being capable of exhibiting high viscosity and minimal flow at the point of application to thus maintain its shape and adherence to the applied structure.